Various communications protocols are known in the art. For example, the Third Generation Partnership Project (3GPP) has been working towards developing a number of protocols for use with a wireless communication path. The original scope of 3GPP was to produce globally applicable technical specifications and technical reports for a 3rd generation mobile system based on evolved Global System for Mobile (GSM) communication core networks and the radio access technologies that they support, such as Evolved Universal Terrestrial Radio Access (EUTRA) including both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) modes. 3GPP's scope was subsequently amended to include the maintenance and development of GSM technical specifications and technical reports including evolved radio access technologies (e.g. General Packet Radio Service (GPRS) and Enhanced Data rates for GSM Evolution (EDGE)). Since then, Fourth Generation (4G) systems have arisen that borrow portions of the protocols from earlier 3G systems.
Presently, EUTRA calls for a random access channel (RACH) protocol and in particular a physical random access procedure requiring reserved resources for RACH access. The RACH channel is used for initial access to the network as well as to transmit small to medium amount of control information and data packets. This 3GPP specification permits an overall procedure that allows for various protocol/operational states to suit varying degrees of needed, anticipated, and/or desired operational activity for transmission of data packets. The RACH (random access channel) is essential for access to the network, for the transmission of control information and data packets. The access channel has different names in different systems, such as RACH in the context of 3GPP and now Long Term Evolution (LTE or 4G), or ranging in the context of IEEE 802.16e and now WiMAX (IEEE 802.16m) using Code Division Multiple Access (CDMA), for example. In the description herein, the LTE implementation of RACH is used, for example, in its general sense to represent the ranging or access channel of various communication systems.
In the current LTE standard, random access consists of a message exchange between a mobile station or user equipment (UE) and a base station or enhanced NodeB (eNB), wherein a UE sends a Preamble or Message 1, and the eNB sends a RACH Response (RAR) or Message 2 acknowledging the Preamble transmission by the UE by indicating in the RAR a unique Preamble identifier associated with each Preamble. Due to scheduling and congestion issues in the downlink eNB is given a window of time to send the RAR. This is defined as a RAR window, which is a window that is configurable between two to ten milliseconds, depending upon the choice of system parameters. The UE is required to monitor the whole RAR window to detect if the eNB has acknowledged its Preamble identifier.
The RAR sent by the eNB is to be received by all UEs that transmitted Message 1 in the current RACH opportunity (i.e. RAR window). However, it is possible that, due to resource limitations in a sub-frame, the eNB sends responses only for a subset of detected Preambles sent by the UEs while the rest of the detected Preambles are acknowledged in subsequent sub-frames within the RAR window for this RACH opportunity. In this case, if the UE did not detect its Preamble identifier in the first Message 2 (i.e. RAR message) it receives, e.g., at the beginning of the RAR window, then the UE will still need to monitor for potential subsequent Message 2s until the end of the RAR window. If the UE does not see its Preamble identifier in any of the Message 2s in the RAR window, it must then restart Random Access Procedure and retransmit its Preamble (i.e. Message 1) again. This continued monitoring until the end of the RAR window by the UE introduces additional delay (e.g. 10 ms) for any UE that would never receive its Preamble identifier in any of the Message 2s within the RAR window and would therefore need to retransmit its Preamble anyway.
Therefore, it would be beneficial if the UE could detect earlier that its Preamble transmission was not received by the eNB (e.g. insufficient Preamble transmission power), or was received by the eNB but the eNB due to congestion or other issues decided not to acknowledge UE's Preamble transmission in message 2, and would therefore not need to wait until the end of the whole RAR window before it can retransmit its Preamble.
Skilled artisans will appreciate that common but well-understood elements that are useful or necessary in a commercially feasible embodiment are typically not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.